The present invention relates to a method and apparatus for producing a tube of a heat-plastified, resinous, mesh film material and, more particularly, to such a method and apparatus in which various tube diameters may be produced, in an improved manner, with the same method and apparatus.
A number of different techniques have been used to form extrudable, synthetic, resinous, thermoplastic compositions into film. Such film finds utility in numerous applications, such as for example as wrapping material, in garbage bags, and the like. It is known that the tear resistance of such film may be increased significantly by incorporating ridges of increased film thickness in the film, producing a product sometimes referred to as mesh film. The ridges may be configured in various patterns, including parallel stripes, criss-cross patterns, and combinations thereof.
U.S. Pat. No. 4,265,853, issued May 5, 1981, to Havens, discloses apparatus for producing a ridge pattern in extruded film by differential cooling of the film during a stretching process. The film is extruded through a tubular die and stretched as it leaves the die. A plurality of nozzles, spaced around the tubular film. rotate around the film as it is stretched, cooling the film to produce a plurality of narrow strips of increased thickness, and achieving a sharply defined ridge effect. A criss-cross pattern of ridges may be obtained by using two sets of nozzles which are rotated around the film in opposite directions. In the Havens U.S. Pat. No. 4,265,853 apparatus, the tubular film passes around the outside surface of a cylindrical cooling mandrel after it is enlarged to its desired diameter. Thereafter, the tubular film is split into two strips of film which are collected for further processing. While providing a reinforced film product of high quality, the Havens U.S. Pat. No. 4,265,853 apparatus is limited in that it is capable of producing tubular film of only a specific diameter. It is seen, therefore, that a need exists for a method and apparatus for making mesh film of various selected diameters without changing the apparatus.